This invention relates generally to concrete, and more particularly to a full strength, low density concrete composition which is especially resistant to cracking and method of making the same.
In the past, there have been many different proposals for making a low density concrete. All of these, however, have resulted in certain serious drawbacks, and hence none have been totally successful. One of the principal ways of approaching the manufacture of low density concrete has been the entrainment of gas or air or some type of an expanded particle as a portion or all of the aggregate. This may take the form of actually whipping the concrete to entrain small air bubbles, or it may take the form of additions of certain open cellular or closed cellular material or may take the form of adding certain chemical substances which upon application of heat and/or reaction agents to liberate a gas. Examples of these are found in U.S. Pat. Nos. 3,272,765 and 3,021,291. These approaches have not been entirely successful, due to several factors. First, the utilization of a more porous material allows for the soaking up of water, which can freeze and cause cracking of the concrete. Also, other disadvantages include the necessity to closely control the additions and certain of the processing conditions in order to obtain the desired results. Other problems include the handling of various reagents, the mixing of reagents and the like, such that the utilization of this type of concrete has been somewhat limited to special circumstances with special handling equipment.
There also have been several attempts to form decorative concrete structures, such as by adding colored chips of natural or synthetic material. While there has been a certain amount of success in obtaining decorative effects this way, nevertheless, the resulting concrete is of a much reduced strength, and generally usable only for minimal structural applications, such as surface facing. Also, with the use of decorative types of material there has often been encountered severe cracking problems of the concrete. Examples of the use of additional material as decorative use in concrete may be found in U.S. Pat. No. 3,778,290.
Further conventional prior art practice utilizing natural aggregate has resulted in somewhat erratic results in the final product due to unwanted impurities in the aggregate while often manifesting itself as cracking or other deficiencies in the final concrete product.
While all these different prior art techniques have found certain limited application, nevertheless, none of them has provided a low density, full strength structural concrete which is resistant to cracking.